CAN Bus Harmonic Compensation Circuit for EMC Emission Control
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Solution Overview
Problem
CAN devices often fail to comply with electromagnetic compatibility (EMC) requirements due to excessive harmonic components in the frequency range of 0.6 MHz to 10 MHz, leading to costly redesigns, particularly in the automotive sector where stringent EMC standards apply.
Innovation Solution
A method and circuit that compensates electromagnetic noise in CAN buses by transmitting a test signal, performing frequency analysis to detect harmonic components exceeding thresholds, and generating anti-phase sinusoidal compensation signals to be transmitted over the bus, using a combination of oscillators, mixers, band-pass filters, and analog-to-digital converters to adjust and phase-shift these signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If filtering capacitors are coupled at the output of the CAN transceiver to reduce electromagnetic emissions, then electromagnetic compatibility is improved, but the EMC performance may still be insufficient and additional complex compensation circuits are required
Solution Approach 1:
The patent implements a feedback mechanism where the transceiver receives the transmitted test signal back, performs frequency analysis to detect excessive harmonic components, and automatically generates compensation signals to cancel out the harmful emissions. This closed-loop feedback system dynamically adjusts the compensation based on actual measured emissions, resolving the contradiction by providing effective EMC performance through intelligent control rather than passive filtering alone.
Solution Approach 2:
The patent introduces an intermediary compensation signal generation circuit that acts as a mediator between the transmitted signal and the harmful emissions. This intermediary system generates anti-phase sinusoidal signals at frequencies corresponding to excessive harmonics, effectively canceling out the harmful electromagnetic emissions without requiring complex passive filtering components.
2Object-affected harmful factors
If the frequency analysis range is increased to detect more harmonic components for compensation, then EMC compliance is improved, but the processing time and computational resources are increased
Solution Approach 1:
The patent segments the frequency analysis process by dividing the frequency spectrum into multiple ranges and using different detection strategies for different segments. The processor prioritizes detection of lower frequency harmonics (up to 10 MHz) which are most critical for EMC compliance, while using more efficient detection methods for higher frequencies. This segmentation allows comprehensive harmonic detection without requiring equally intensive processing across the entire frequency spectrum.
Solution Approach 2:
The patent performs preliminary frequency analysis during the test signal transmission phase, identifying excessive harmonic components before final compensation is applied. By pre-detecting which harmonics exceed thresholds and need compensation, the system can prepare compensation signals in advance, reducing the overall processing time required for EMC compliance verification.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively reduces electromagnetic emissions to comply with EMC standards, minimizing the need for costly redesigns by continuously compensating 'faulty' harmonics, thereby enhancing the electromagnetic compatibility of CAN devices.
Implementation Method 1
mixing each of said sinusoidal signals sequentially generated with the test signal received after propagation over the CAN bus, thereby sequentially generating a set of mixed signals
Implementation Method 2
applying band-pass filtering at a fixed frequency to the mixed signals in said set of mixed signals, thereby sequentially detecting said set of harmonic components
Implementation Method 3
generating and transmitting over the CAN bus a set of compensation signals, each compensation signal in the set of compensation signals being a sinusoidal signal having a respective frequency equal to one of the frequencies stored, and being in anti-phase with respect to the harmonic component of the test signal received having said respective frequency
Data Source
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AI summary
A method of compensating electromagnetic emissions of a device (D) for use in a CAN bus (B) is described. The device (D) comprises a CAN transceiver (300) coupling the device (D) to said CAN bus (B) for transmitting and receiving signals. The method comprises: - transmitting a test signal (TS1) over the CAN bus (B), - receiving, at the device (D), said test signal after propagation over the CAN bus (B), - performing frequency analysis processing (OSC2, 304, 306) of the test signal received to detect a set of harmonic components of the test signal received having an amplitude exceeding a certain threshold (VOEM,th), - storing (316) respective values of frequency of harmonic components in said set of harmonic components having an amplitude exceeding said certain threshold (VOEM,th), and - generating and transmitting over the CAN bus (B) a set of compensation signals, each compensation signal in the set of compensation signals being a sinusoidal signal having a respective frequency equal to one of the frequencies stored, and being in anti-phase with respect to the harmonic component of the test signal received having said respective frequency.